Continuous press for curing scarfed veneer joints



Dec; 2, 1969 H. A. KELLER 3,481,376

CONTINUOUS PRESS FOR CURING SCARFED VENEER JOINTS 4 Sheets-Sheet 1 Filed July 31, 1967 INVENTOR. IMQOLD A- kA'LLER BY MMe li H. A. KELLER CONTINUOUS PRESS FOR CURING SCARFED VENEER JOINTS 4 Sheets-Sheet 2 ILW I INVENTO HAEOLD A. kELLE wnmutgvlm Dec. 2, 1969 Fil-edJuly 31, 1967 Dec. 2, 1969 H. A. KELLER 3,481,376

CONTINUOUS PRESS FOR CURING SCARFED VENEER JOINTS Filed July 51, 1967 '4 Sheets-Sheet 5 INVENTOR. lMkOLD A. xnuk BY (.JQMAA-SJM ATTYS United States Patent 3,481,376 CONTINUOUS PRESS FOR CURING SCARFED VENEER JOINTS Harold A. Keller, Clarkston, Wash., assignor to Pollatch Forests, Inc., Lewiston, Idaho, a corporation of Delaware Filed July 31, 1967, Ser. No. 657,098 Int. Cl. B27d 3/00 US. Cl. 144-281 16 Claims ABSTRACT OF THE DISCLOSURE A reciprocating press is described that moves back and forth along a continuous line of moving overlapped scarfed veneer sheets to apply pressure to the overlapped scarfed ends as the sheets are moved forward to cure the glue therebetween. After the glue is cured, the press is released and reciprocated rearward to apply pressure to subsequent overlapped scarfed ends.

BACKGROUND OF THE INVENTION This invention relates to continuous presses and more particularly to continuous presses for curing the glued scarfed joints of continuously moving overlapped wood veneer sheets.

Generally, heretobefore a continuous strip of wood veneer was produced by first forming beveled surfaces on the ends of the sheets (generally referred to as scarfing) and then manually aligning the sheets in an overlapping manner. The overlapping ends were then placed in a stationary press to cure the glue to form a rigid joint between the sheets.

The prior art includes an apparatus for joining scarfed veneer ends in which the preceding sheet is held stationary while the succeeding sheet is moved forward against alignment stops to accurately position the forward scarfed end of the succeeding sheet over the trailing scarfed end of the preceding sheet. The sheets are then independently gripped and transported to a stationary press where the sheets are stopped and aligned with the press. The press applies pressure and heat to the overlapped ends to form a joint between the sheets.

The length of the strip of veneer sheets that may be joined by such an apparatus is substantially limited. Each time a sheet is to be added, the preceding sheets are stopped to permit the addition. This requires the acceleration and deceleration of the joined sheets which necessitates very complicated and expensive equipment to perform. The longer the line of joined sheets the more difficult the problem becomes.

It is recognized that it would be extremely advantageous and considerably more economical to be able to form a continuous strip of veneer sheets in a continuously moving process without having to stop the strip to add an additional sheet or to cure the joints.

One of the limiting components in attempting to efficiently produce a continuous veneer strip is the curing press itself. Considerable development was conducted in attempting to construct a continuous press that could satisfactorily and economically cure the glued joints while the sheets are moving. 7

Continuous presses are not new to the lumber or plywood industries as continuous presses have been used for continuously pressing laminated sheet material to form plywood or laminated beams. Basically, the different types of continuous presses fall into three general categories: (1) the roller press where the sheets or laminae are fed through rotating rollers to press the sheets together to cure the glue, (2) conveyor type presses having 3,481,376 Patented Dec. 2, 1969 opposing endless pressure bands with pressure plates biasing the adjacent band flights to press the moving sheets, and (3) a reciprocating press that grips one section at a time and moves therewith to cure the glue and then releases the section and returns to grip a succeeding section.

One of the principal disadvantages of the first type of press is that the rollers have a small area of pressure contact with the sheet material and are unable to apply a pressure for a sufficient period to adequately cure the glue. Another disadvantage of the roller type press is that it is difiicult and expensive to provide means to heat the rollers to efficiently cure the glue.

An example of the second category of presses is illustrated in the Schubert Patent No. 3,111,149. Although the conveyor type of continuous press is widely used for pressing veneer sheets to form plywood it has many disadvantages for application in pressing scarfed joints of veneer sheets. One of the principal disadvantages is that the pressure is applied over a much larger area than is necessary to cure the joints. This means that a considerable amount of the pressure area is ineffectively utilized and provides an inefficient pressing system.

An example of the third type of press is shown in the Alenius Patent 3,202,090 in which a reciprocal carriage supports the pressure platens. One of the principal problems heretofore associated with reciprocal type presses has been involved in the drive means in being able to accelerate and deaccelerate the carriage with sufficient precision to accurately position the platen members with relationship to the sheet. Generally the carriage platen structure is extremely heavy and requires very complicated and expensive drive equipment, Frequently the inadequacy of such a reciprocal press is clearly demonstrated by the inordinant number of repairs that need to be made to keep it operating.

One of the principal objects of this invention is to provide a reciprocal press apparatus that is capable of efiiciently and economically curing the scarf joints of a continuous veneer strip while the strip is moving.

An additional object of this invention is to provide a chain drive system for moving the reciprocal press forward which minimizes chain wear.

A further object of this invention is to provide a new and novel sheet drive system mounted on the reciprocal carriage for moving the sheet forward at a prescribed speed independently of whether the carriage is stationary or moving forward or back.

An additional object of this invention is to provide a reciprocal continuous press that is efficient in operation, simple in construction and economical to operate.

A further object of this invention is to provide a simple and effective return drive for returning the carriage to the starting position.

Additional objects and advantages of this invention will become apparent upon reading the following description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of this invention is illustrated in the accompanying drawings, in which:

' FIG. 1 is a perspective schematic view showing the overlapped ends of veneer sheets being cured in a reciprocal continuous press incorporating the principal features of this invention;

FIG. 2 is a side elevation view of the continuous press;

FIG. 3 is a plan view of the continuous press;

FIG. 4 is a front elevation view of the reciprocal carriage of the continuous press; and

FIG. 5 is a cross sectional view taken along line 55 in FIG. 4.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT There is shown schematically in FIG. 1 an apparatus for curing scarf joints of overlapping sheets of wood veneer forming a strip. For illustration purposes, reference will be made to only two sheets 20a and 20b although it should be appreciated that the sheets 20a and 20b comprise only a section of the continuous veneer strip. As best seen in cross-section in FIG. 5, the sheet 20a has an upwardly facing beveled surface B formed on the trailing end thereof. The veneer sheet 20b has a downwardly facing beveled surface A that overlaps the beveled surface B of sheet 20a. Although not shown in any detail, glue has been applied between the surfaces A and B at a previous station. The continuous strip is assembled from individual veneer sheets in an upstream station and propelled onto the joint curing apparatus at a prescribed speed.

The joint curing apparatus is generally identified by numeral 300 and includes a base frame 301 with frame uprights 302, 303 and 304 that may be seen in FIG. 2. Parallel longitudinal crane rails 307 and 308 are supported between the uprights 302 and 303 by transverse brackets 305 and 306 affixed to the uprights 302 and 303 respectively. Parallel longitudinal channel irons 310 and 311 are mounted between the uprights 303 and 304 at an elevation above the crane rails 307 and 308 as may be seen in FIG. 2.

The apparatus 300 includes a reciprocal carriage 315 that is reciprocally mounted on the rails 307 and 308 for movement between the uprights 302 and 303. The carriage 315 includes a carriage frame 316 that has spaced side channels 317 and 318 that are parallel to one another as may be particularly seen in the front view, FIG. 4. The carriage frame 316 also includes a fixed bottom platen 319 that is mounted between the side channels 317 and 318. An upper platen 320 is movably mounted immediately above the bottom platen 319 for grasping the overlapped scarfed sheet ends therebetween.

The bottom platen 319 as shown in cross section in FIG. 5, includes a transverse horizontal beam 321. An insulation layer 322 is mounted on the beam 321 for insulating the heat generated by the platen elements from being communicated to the rest of the carriage structure. A backing plate 323 is mounted on the insulation layer 322 for supporting the curing elements of the bottom platen. The curing elements of the bottom platen include two spaced cold platen elements 324 and 325 that are mounted parallel to each other across the carriage on the backing plate 323. Intermediate and spaced from the cold platen elements, is a hot platen element 326 heated by conventional means to a temperature of approximately 400 F. for curing the glue between the scarfed surfaces A and B. Two spring biased transverse strippers 327 and 328 are mounted on opposite sides of the hot platen member 326 for stripping the joint from the hot element. Each stripper includes studs 333 that are mounted upright on the base plate 323. Springs 331 are mounted about the studs 333. Channel caps 332 are secured to the top of the springs 331 for engaging the sheets spaced from the overlapped portion of the joint.

As viewed in FIG. 4, upwardly and outwardly extend- I ing brackets 334 are mounted to the side channels 317 and 318 for supporting the trunnions of hydraulic actuators 335. The actuators 335 move the upper platen 320 up and down. Connecting rods 336 of the actuators extend upwardly to connecting blocks 337 afiixed to the upper platen by brackets 338.

The upper platen 320 includes an upper platen beam 340 that extends transversely over the sheets between the actuators 335. Self-centering washer bearings 341 (FIG. 5) are fixed at intervals along the base of the platen beam 340 for supporting the curing elements of the upper platen. The self-centering washer 341 permits angular movement of the upper curing elements fore and aft to adjust to the contour of the joint to apply a uniform pressure to the joint. Each of the self-centering washer bearings 341 in cludes a stationary race 344 and a slidable mounted race 345 that is complementarily contoured to slide on the stationary race 344. A plate 343 is attached to the selfcentering washer bearings 341 by bolts 342. An insulation strip 346 is positioned below the plate 343 to prevent the heat that is generated from the curing elements from being communicated to the carriage structure. A backing plate 347 is mounted below the insulation of the strip for supporting the curing elements of the upper platen.

The curing elements of the upper platen include two parallel cold platen elements 348 and 350 that are vertically aligned with the corresponding cold platen elements 324 and 325 respectively of the lower platen. A hot platen member 351 is positioned intermediate the cold platen members 348 and 350 in vertical alignment with the bottom hot element 326 for engaging the joint area to cure the glue and form a secure and rigid joint.

- The hot plenum element is heated by conventional means to a temperature of approximately 400 F.

Stripper members 352 and 353 similar to stripper members 327 and 328 are positioned intermediate the cold platen members 348 and 350 and the hot platen element 351 for stripping the joint from the hot platen member 351 when the upper platen is elevated at the completion of the curing cycle.

As may be particularly seen in cross section in FIG. 5, throat members are positioned immediately upstream of the platen members for guiding the sheets as they move between the platen members. The throat members include a stationary throat member or deflector 355 that extends transversely across the front of the carriage above the path of the sheets. The stationary throat member 355 is supported by rods 356 that project upwardly from the side channels 317 and 318. A resiliently biased throat member or deflector 357 is positioned immediately below the stationary throat member 355 for supporting the sheets as they are presented to the platen members. The throat member 357 is pivotally mounted on a shaft 358. The shaft 358 is mounted in bearings 360 that are attached to the side channels 317 and 318. The back of the deflector 357 is supported on springs that surround rods 361 that project upwardly from the channels 317 and 318.

The carriage 315 is supported on the crane rails 307 and 308 by wheels 365. The forward set of wheels 365 are free wheeling on a front axle 366. The rear wheels are free wheeling on the rear axle 367. The axles 366 and 367 are rotatably mounted in bearing blocks 368 that are affixed to the underside of the side channels 317 and 318 (FIGS. 4 and 5). Guide rollers 370, that may be seen in FIG. 4, extend from the side of the side channels 317 and 318 for engaging the inside of the rails 307 and 308 to laterally position the carriage on the rails and to provide lateral stability as the carriage moves along the rails. Brackets 371 (FIGA) are aflixed to the underside of the channels 317 and 318 and project downwardly for supporting pillow blocks 372. The pillow blocks 372 support a rotatable shaft 373 at an elevation below the shafts 366 and 367. Electrically operated brakes 375 and 376 are rigidly mounted to the brackets 371 and surround respective ends of the shaft 37 3. When activated, the brakes 375 and 376 stop the rotation of the shaft 373. A metal apron 377 (FIG. 4) extends across the carriage between the brackets 371 for providing structural rigidity.

Two chain sprockets 379 (FIG. 4) are keyed to the shaft 373 intermediate the pillow blocks 372 and the electrically operated brakes 375 and 376 respectively. Two chain sprockets 380 are keyed to the front axle 366 intermediate the pillow blocks 368 and the front wheels 365 in lateral alignment with the sprockets 379 respectively. Similar chain sprockets 381(FIG. 3) are keyed to the rear axle in lateral alignment with the sprockets 379 and 380.

The press carriage 315 is driven in the direction of flow of the sheets by continuously moving parallel endless drive chains 382 and 383. The upper flights of the chains 382 and 383 move forward in the same direction as the flow of the sheets. The upper flights of the chains 382 and 383 engage the sprockets 379, 380 and 381. Specifically the upper chain flights round sprockets 380 and are directed downwardly around the sprockets 379' and then back over the sprockets 381 before proceeding rearward from the carriage.

Each of the drive chains 382 and 383 are movably supported by idler sprockets 384 and tension adjusting sprocket 385 (FIG. 2) that are rotatably mounted on the uprights 302. Idler sprockets 386: are mounted near the base of the upright 303 for engaging the drive chains 382 and 383. The drive chains 382 and 383 are driven by drive sprockets 387 that are affixed to a shaft 388 that is rotatably mounted in bearings on the upright 304 (FIG. 4).

To make sure that there is no slack in the upper flight of the chains 382 and 383 that could adversely affect the accuracy of the apparatus, support races 390 and 391 are positioned between the carriage and the drive sprockets 387. Support races 390 and 391 are attached to the rear of the carriage 315 and extend rearward underneath the upper flight of the chains 382 and 383. The races are slidably supported in channel bearings 392 (FIGS. 1 and 2). Idler sprockets 395 are rotatably mounted immediately above the channel bearings 392 to change the direction of the upper flight of the chains. The support races 391 are aflixed at an incline from the idler sprockets 395 to the drive sprockets 387. Support races 391 are supported on brackets 396 attached to the frame channels 310 and 311 as shown in FIG. 2.

The apparatus has a sheet drive means mounted on the carriage for moving the sheet forward independently of whether the carriage 315 is stationary or moving forward or back. The sheet drive means includes a drive roller 400 (FIGS. 1 and 5) that is rotatably mounted immediately behind the platen 319. The drive roller 400 is secured to a shaft 401 (FIG. 5) rotatably mounted in bearing pillow blocks 402 on the upper surfaces of the channels 317 and 318. Sprockets 403 are affixed to the ends of the shafts 401 in alignment with sprockets 405 that are keyed to the rear axle 367. Since the sprockets 381 and 405 are keyed to axle 367, the rotation of one is transmitted to the other. A chain 404 extends between the sprockets 403 and 405 for transmitting rotational movement therebetween. The sprockets 403 and 405 may be considered a drive train between the transverse axles 367 and 401. As may be particularly seen in FIGS. 1 and 5 a pressure roller 406 is affixed to a rotatable shaft 407 that is mounted to brackets 408. The brackets 408 are pivotally mounted to frame extension 409 at the rear of the carriage frame 316. The pressure roller 406 biases the sheets into engagement with the drive roller 400 for moving the sheet forward at a rate equal to the speed of the chains 382 and 383.

The joint curing apparatus has a separate drive mechanism that moves the carriage 315 back to the starting position. The reverse drive means includes two spaced parallel pneumatic cylinders 411 and 412 (FIGS. 1 and 3) that are mounted on the longitudinal channels 310 and 311 respectively. Pneumatic cylinders 411 and 412 have piston rods 413 and 414 respectively that extend forward and are connected through brackets 415 to the rear of the carriage frame. The pneumatic cylinders 411 and 412 are pressurized by a pneumatic pressure system at a substantially constant pressure, so that when the electrically operated brakes 375 and 376 are released, the pneumatic cylinders will drive the carriage rearward to the starting position. The pneumatic system that pressurizes the cylinders 411 and 412 is generally part of a plant pneumatic system so that the pressure will remain substantially constant independently of the position of the piston. However, if a plant or central pneumatic system is not available accumulators may be attached to the system to provide a constant pressure. By providing constant pressure on the pistons, complicated pneumatic control systems are not needed. Dash pots 417 (FIG. 3) are mounted on the upright frame 302 for stopping the carriage as it is moved to the starting position.

Expandable support means are connected between the uprights 302 and 303 and the carriage 315 for supporting the veneer sheets as the carriage moves back and forth on the crane rails. The expandable support means includes an expandable pantographic front frame 420 and an expandable pantographic rear frame 421 (FIG. 1). Expandable front frame 420 includes two sets of interconnected levers 422 and 423 that may be seen in plan view in FIG. 3. The expandable rear frame 421 also includes two sets of interconnected levers 424 and 425. Contoured transverse sheet metal frames 426 are mounted on the upper joining ends of the levers to form moving support for the veneer sheets as the carriage moves back and forth on the crane rails.

A belt system is mounted partly on the frame 301 for receiving the sheets from the joint curing apparatus 300. The belt system includes a belt 430 (FIG. 2) and moves over an idler roller 431 that is rotatably mounted on the uprights 303.

To properly coordinate the speed of the sheets as they are fed to the apparatus 300 With the speed of the chains 382 and 383, an interconnected drive means may be provided. As an alternate drive means separate variable speed motors may be provided that are synchronized together through a conventional main control system for coordinating the speed in which the sheets are fed onto the apparatus 300 and the speed of the drive chains 382 and 383. The control system may be capable of uniformly increasing and decreasing the speeds as desired. In this particular embodiment, as shown in the drawings, the entire system including the apparatus 300 is driven from a common drive shaft that is rotated by a motor 445 (FIG. 3). The speed of the motor 445 is reduced by a gear reduction unit 446. The shaft 447 from the unit 446 extends to a right angle gear. One segment of the shaft 46 extends downstream for driving the belt 430. Another segment of the shaft 46 extends upstream to other stations for performing various functions including the moving of the sheet to the apparatus 300.

A sprocket 450 is mounted on the drive shaft 447 for moving a chain 451 to rotate the sprocket 452 that is affixed to the joint curing apparatus drive shaft 388.

For purpose of illustration, the operation of the apparatus 300 will be described with reference to veneer sheets 20a and 20b. The sheets 20a and 20b are fed to the apparatus 300 with their ends overlapped at a predetermined speed equal to the speed of the chains 382 and 383. When the overlapped surfaces A and B of the sheets 20a and 20b are vertically aligned with the hot platen members 326 and 351, the electrically operated brakes 375 and 376 are actuated by a conventional timing control system to prevent further rotation of the shaft 373. Since the chain sprockets 379 are keyed to the shafts 373, the carriage becomes locked to the moving drive chains 382 and 383 thereby causing the carriage to move forward at the speed of the chains. The hydraulic actuators 335 are then operated by the conventional control system to lower the upper platen to press the surfaces A and B together to cure the glue therebetween. Cold platen members 324, 325, 348 and 350 engage the sheets spaced from the scarfed surfaces A and B to hold the sheets in relationship to each other so that there is no movement therebetween while the glue is being cured and to also limit the downward movement of the upper platen to apply a uniform pressure to the joint area. The hot platen members, which are heated to a temperature of approximately 400 F., engage the sheets in vertical alignment with the surfaces -A and B to cure the glue therebetween to form a rigid scarfed joint. The platen elements apply a curing pressure of approximately 200 p.s.i. to the joint area.

The duration in which pressure is applied to the joint by the carriage platens is principally determined by the curing rate of the particular glue under the particular conditions. Thus, if fast curing glue is utilized, the duration of the pressure and heat application can be shorter than if slower curing glue is used. From experimentation, it can be determined what is the optimum duration for maximum production. At the end of the curing period, the conventional control system activates the hydraulic cylinders 335 to lift the upper platen 320. The spring biased strippers 327, 328, 352 and 353 strip the joint from the hot platen to prevent any sticking that might otherwise occur. Immediately thereafter, the electrically operated brakes 375 and 376 are activated by the control system to permit the rotation of shaft 373 thereby enabling the pneumatic cylinders 411 and 412 to move the carriage in its return direction to receive the succeeding overlapped ends.

When the carriage is moving forward, the sprockets 381 are not rotating and thus no rotational movement is imparted to the sheet drive means 400. However, on the return stroke the sprockets 381 are rotated at a speed related to the forward movement of the chains 382 and 383 plus the return movement of the carriage. This rotation is transmitted to the drive roller 400 to provide a positive drive means for moving the strip forward as the carriage is moving backward. Thus it can be said that the curing machine has a sheet drive means that moves the strip forward independently of whether the carriage is stationary or moving in a forward and return direction. From the carriage the strip moves onto the belt 430 to be conveyed downstream for further processing.

One can appreciate from the structure shown in this embodiment that the carriage 315 is lightweight and minimizes the driving forces required in accelerating and decelerating the carriage as it is moved back and forth on crane rail.

One of the very important features of this apparatus is the provision that minimizes the wear of drive chains 382 and 383. This is accomplished by providing a chain that continuously moves in the same direction so that when the brakes 375 and 376 are operated the same section of the chain is seldom engaging the sprockets 379. Thus the same section of chain is not continually subjected to the forces inherent in the continual acceleration movement of the carriage from the starting position.

It should also be appreciated that the apparatus 300 is extremely accurate in being able to repeatedly move the carriage forward in alignment with the overlapped scarfed end surfaces so that the platens are vertically aligned with the joint.

What is claimed is:

1. An apparatus for receiving and pressing continuously moving sheet material, comprising:

(a) a stationary base frame;

(b) a track mounted on the base frame parallel to the path of the sheet material;

(c) a press carriage mounted on the track for reciprocal movement;

(d) pressing means mounted on the carriage for pressing the moving sheet material therebetween;

(e) a continuously moving endless drive chain mounttd on the base frame adjacent to and parallel with the track in which one flight thereof moves forward at a speed equal to or greater than the speed of the sheet material;

(f) actuator means mounted on the carriage and operatively connected to the pressing members for closing the pressing member-s against the sheet material for a selected pressing time period and then releas ing the material at the end of the selected pressing time;

g) locking means mounted on the carriage for locking the carriage to said forward moving chain flight to move the carriage forward at the same speed as the chain for a period of time equal to or greater than the selected pressing time period and then unlocking the carriage from the moving chain; and

(h) a carriage drive means mounted on the base frame that is rendered effective upon the unlocking of the carriage from the moving chain for returning the carriage to a starting position.

2. The apparatus as defined in claim 1 wherein the press carriage has a rotatable shaft with a sprocket affixed thereon in engagement with the forward moving chain flight and wherein the locking means includes a brake mounted on the shaft for selectively preventing the rotation of the shaft to cause the carriage to move with the chain flight.

3. The apparatus as defined in claim 1 further comprising a sheet material drive means mounted on the carriage and operatively connected to the forward chain flight for supporting and moving the sheet material forward at the speed of said chain flight independently of whether the carriage is stationary or moving forward or back.

4. The apparatus as defined in claim 3 wherein the sheet material drive means includes:

(a) a first transverse shaft rotatably mounted on the carriage;

(b) a roller affixed to the first shaft for engaging and supporting the sheet material;

(c) a second transverse shaft rotatably mounted on the carriage;

(d) a sprocket affixed to the second transverse shaft engaging the forward continuously moving chain flight; and

(c) drive train interconnecting the first second shaft for transmitting the rotation of the second shaft to the first shaft to drive the sheet material forward at the same speed as the chain independently of whether the carriage is stationary or moving forward or back.

5. The apparatus as defined in claim 1 wherein the pressing members include a vertically movable upper platen assembly and a stationary lower platen assembly that span across the sheet material and wherein each of the platen assemblies includes:

(a) a transverse hot platen element that extends across the sheet material; and

(b) resiliently biased stripper elements alongside the hot platen element for stripping the sheet material from the hot platen element.

6. The apparatus as defined in claim 1 further comprising an expandable pantographic frame assembly mounted between the stationary base frame and the reciprocal carriage for supporting continuously moving sheet material.

7. The apparatus as defined in claim 1 further comprising chain support races for supporting said moving chain flights forward of the carriage to prevent slack therein.

8. An apparatus for receiving and curing glued joints of a continuously moving strip of overlapped wood sheets, said apparatus comprising:

(a) a stationary base frame;

(b) spaced rails mounted on the base frame parallel with the path of the strip;

(c) a press carriage mounted on the trails for reciprocable movement between a starting position and a downstream position, said carriage having transversely spaced rotatable sprockets affixed thereon;

(d) pressing members mounted on the carrage for pressing the joints therebetween to cure the glue;

(6) two spaced endless drive chains continuously moving in one direction on the base frame adjacent to and parallel with the rails, in which upper flights of said chains move forward engaging the sprockets at a speed equal to or greater than the speed of the moving strip to move the carriage forward from the 9 starting position when the carriage sprockets are prevented from rotating;

(f) brake means mounted on the carriage and operatively connected to the sprockets for preventing the rotation of the sprockets to cause the drive chains to move the carriage forward from the starting position at said speed to the downstream position and for releasing the sprockets to permit the rotation thereof at the downstream position;

(g) actuator means mounted on the carriage and operatively connected to the pressing members for closing the pressing members for a prescribed time period during the forward movement of the carriage and for opening the pressing members at the termination of the prescribed time period; and

(h) a return drive means mounted on the base frame which is rendered elfective upon the release of the sprockets at the downstream position for moving the carriage from the downstream position to the starting position.

9. The apparatus as defined in claim 8 further comprising a sheet material drive mounted on the carriage operatively connected to the drive chains for moving the sheet material forward from the carriage at a speed proportional to the speed of the chains independently of whether the carriage is stationary or moving forward or back.

10. The apparatus as defined in claim 8 wherein one of the pressing members includes a hot platen element for heating the joint while pressure is being applied to cure the glue to form a rigid joint.

11. The apparatus as defined in claim 10 wherein resiliently biased stripper elements are mounted adjacent the hot platen for preventing the wood sheets from sticking to the hot platen elements.

12. The apparatus as defined in claim 11 wherein the pressing members include an upper platen assembly that is vertically movable in relation to a lower platen assembly to press the joint therebetween and wherein further the upper platen assembly has a beam that extends transversely over the moving strip with the hot platen element and the stripper elements pivotally mounted to the underside thereof by self-centering bearings to enable the application of the uniform pressure to the joint area.

13. The apparatus as defined in claim 8 wherein the carriage has a throat assembly mounted transversely across the carriage in front of the pressing members to present the strip between the pressing members.

14. The apparatus as defined in claim 8 wherein the sheet material drive comprises:

(a) a first transverse drive shaft rotatably mounted on the carriage downstream behind the pressing mem bers;

(b) a roller fixed to the shaft engaging the strip;

(0) a second transverse shaft rotatably mounted on the carriage adjacent the upper flight of the drive chains;

(d) sprockets aflixed to said second shaft engaging said drive chains; and

(e) a drive train interconnecting the first second transverse shafts for transmitting rotational movement therebetween for moving the sheet material forward at the same speed as the chains.

15. The apparatus as defined in claim 8 further comprising expandable pantographic frames connected between the carriage and the base frame for presenting the horizontal supports for the sheets between the carriage and base frame.

16. The apparatus as defined in claim 8 wherein the carriage return drive includes:

(a) an elongated pneumatic position cylinder mounted on said base frame with a connecting rod attached to the carriage; and

(b) a pneumatic pressure system connected to the piston cylinder for biasing the connecting rod outwardly at a substantially constant force for returning the carriage to the starting position when the pressing members are open and the braking means is released.

References Cited UNITED STATES PATENTS 1,702,185 2/1929 Weber 144-281 X 3,131,737 5/1964 Pearl .1 144-281 3,202,090 8/1965 Alenius 156583 X ANDREW R. JUHASZ, Primary Examiner GIL WEIDENFELD, Assistant Examiner U.S. Cl. X.R. 

